254 COMPARISON OF ARCTIC AND ANTARCTIC DISTURBANCES. 



in H at Matotchkin Schar, which according to Plato II extended from about 18h. 10m. to 18h. 35m., 

 and which w. I lately followed by a movement in the opposite direction, of so closely similar 



s character as to suggest its being an essential part of the same phenomenon. The significance of this 

 will appear presently. 



The Antarctic curves were fairly quiet, according to the Antarctic standard, until about 17h., but the 

 H curve shows a prominent bay from about 12h. 13m. to 13h. 57m., the element being depressed and 

 the minimum coming at about 13h. 18m. The fall and rise were each about 60y. 



During part of the time covered by the H bay there was also a bay on the D curve, a rise of 58' being 

 followed by a fall of 45', and the maximum coming at about 12h. 53m. 



As 1' in D represents a force of about r9y, the D movement was really the larger as well as the more 

 rapid, but owing to the high sensitiveness of the H magnetograph the H movement appeals more to the 

 eye. During the occurrence of the bays on the D and H curves the V trace shows numerous small 

 oscillations of an irregular character, bearing no obvious relationship to the D and H changes, and not so 

 suggestive of the " special type of disturbance " as the H trace is. 



These D and H movements are synchronous with the " polar " storm of Section (i). Also, whilst there is 

 no conspicuously rapid initial movement, the time of commencement is at least very approximately the 

 same as that of the small sudden movement seen at Kew and elsewhere. 



After 17h. the Antarctic curves certainly deserve to be called disturbed. The H trace showed the 

 following changes, superposed on which were the usual short-period smaller oscillations : 



17h. lira, to 17h. 16m. fall 28y, 



17h. 16m. 17h. 20m. rise 23y, 



17h. 20m. 17h. 31m. fall 40y, 



17h. 31m. 17h. 42m. rise 45y, 



17h. 42m. 17h. 53m. fall 41y. 



D showed a number of small oscillations, but none conspicuously large ; it increased, however, 90' 

 between 16h. 53m. and 18h. 3m., going off the sheet at 18h. 3m. for a few minutes. During this time V 

 rose and fell only about lOy, though there were numerous small oscillations. The above movements 

 seem to be associated. They are synchronous with the earlier part of BIRKELAND'S Section (ii), but also 

 with the end of his Section (i). They are followed by a larger H movement. 



Commencing to rise at about 18h. 21m., H, after increasing 74y, got off the sheet at 18h. 27m. Re- 

 appearing at ISh. 31m., in the next 29 minutes it fell 108y, going beyond the limit of registration on the 

 negative side. D commenced to fall at 18h. 21m., when H began to rise, and in the course of 26 minutes 

 fell 61' and rose 70'. During this time V oscillations, though numerous, were small. The form of the 

 Antarctic curves suggests that the phenomena from 18h. 21m. to 19h. Om. were associated together, and 

 the most natural inference seems to be that they form part of the disturbance which BIRKELAND regards 

 as the first " intermediate " storm of his Section (iii). This was the time, it may be added, of one of the 

 most prominent movements seen at BIRKELAND'S co-operating stations. 



The next movements in the Antarctic worth mentioning were fairly synchronous with BIRKELAND'S 

 second "intermediate" storm (20h. 45m. to 21h. 20m.) They are somewhat imperfectly shown, owing to 

 lack of trace. Between 20h. 40m. and 21h. 3m. H fell 45y and rose 50y (possibly more, as the trace is 

 very faint and part may be invisible). The D trace, which had gradually got off the sheet on the positive 

 side, suddenly re-appeared at 20h. 51m. and fell 58' in 6 minutes. After a minor oscillation it began to 

 rise rapidly at 21h. 6m., rising 55' before it again went off the sheet at 21h. 15m. During this time there 

 were some very rapid movements in V; the total range between 20h. 46m. and 21h. 3m. was 22y. 



There was no Antarctic trace from 23h. 20m. to 23h. 45m. on the llth. Between 23h. 48m. and 

 Oh. 31m. on the 12th a bay appeared in the V trace, the maximum depression being about 12y. There is 

 a synchronous bay in the D curve, a fall of 43' being followed by a rise of 33'. The H trace was 

 off the sheet practically all the time. The above D and V movements occur simultaneously with 

 BIRKELAND'S third " intermediate " storm. They are by no means of an outstanding character and do 

 not appeal much to the eye. They are followed, however, by a relatively quiet time. 



